Dual phototube X-ray timer for selective exposure of chest films



1949 R. H. MORGAN ET AL 2,486,866

DUAL PHOTOTUBE X-RAY TIMER FOR SELECTIVE EXPOSURE OF CHEST FILMS Filed May 15, 1946 1 Husel/ HMorgan V Paul ct Hod es 12;; .flwik -2 Patented Nov. 1, 1949 DUAL PHOTOTUBE X-RAY TIlVIER FOR SELECTIVE EXPOSURE F CHEST FILMS Russell H. Morgan and Paul C. Hodges, Chicago, 111., assignors to the United States of America as represented by the Secretary of War Application May 15, 1946, Serial No. 669,820

1 Claim.

This invention relates generally to a method and means for photographing the lungs in which exposure of the X-ray films is controlled by the translucency of the normal lung, and more particularly it is directed to an X-ray tuning mechanism by which the X-ray exposure of chest films may be controlled photoelectrically to produce films of optimum density of either the right lung or of the left lung or of the least radiopaque lung.

The device is desirable for use in chest radiography because under normal circumstances a normal lung is the least radiopaque lung and when a pathological condition is located on one side it is desirable that the normal side be properly exposed or at least control the density of the film so that the abnormal lung may produce on the film a density which may be compared with the density of the normal lung as appearing in the standard X-ray film.

One object of the invention is to provide a device for simultaneously photographing both lungs by X-ray and terminating the radiation on completion of the required exposure of the more translucent lung.

Another object of the invention is to provide an automatic photoelectric tuning mechanism whereby in chest radiography it is possible to control exposure by the radiation passing through the right lung or the left lung, or the more radiolucent of the two lungs, so that the pathological condition of the infected lung may be compared to the normal lung to determine the degree of infection.

Other objects and advantages will become apparent as the invention is more fully disclosed.

Referring to the accompanying drawing which illustrates diagrammatically the circuit and various elements of the invention the numeral l indicates an X-ray tube, '2 a grid, 3 the patient whose lungs are being photographed, 4 the photographic film and 5 and '6 fluorescent screens, adjacent the fluorescent screens are placed the two phototubes II and I! which are connected respectively to two amplifier tubes I3 and I8 and two thyratrons l6 and 2!. The condenser 12 is connected between the control grid 130 of cathode I 3d of the amplifier tube l3 through the grid bias resistor M. In parallel with the condenser 12 is a normally-closed pair of contacts d of the relay 25. The plate |3a of the amplifier I3 is connected to the grid 16b of the thyratron l6 and is in series with the resistor l5 which in turn is connected to terminal 30. The cathode llic of the thyratron I6 and one end of the resistor M are connected to terminal 29. Between terminals 29 and 30 is applied a -125 volt D. C. potential. The plate lBa of thyratron I6 is connected in series with the normally-open contact 251) of the relay 25 and the field coil of a D. C. relay '22 to terminal 30. The operation of the amplifier l3 is stabilized by maintaining the screen grid I3b of the amplifier l3 at constant potential by means of the voltage regulator tube 23 and the resistor 24.

The relay 22 possesses a pair of normally-closed contacts 22a which are in series with a pair of normally-open contacts 25a of the relay 25. These two sets of contacts are connected to terminals 3i and 32 and constitute a switch by means of which power may be applied to the field coil of the contactor relay 33 of the X-ray machine and when power is applied to this field coil the contactor 34 is closed and the X-ray machine thereby energized. The field coil of the relay 25 is connected in series with the switch 26 through the terminals 3! and. 32 to a l10-volt alternating current voltage supply. A high-voltage D. C. supply is applied between terminals 35 and 36. In series with terminal 36 is the variable resistor 31 and resistor 38 by which the dynodes of the phototube H receive the proper voltages for operation of this tube.

The anode lla of the phototube I! is connected to the condenser 48 and to the grid of the amplifier l8. Condenser 40 is connected between the grid lBe and the cathode "3d of the amplifier l8 through the grid bias resistor [9. The plate Ilia of the amplifier I8 is connected to the grid Zlb of the thyratron 2! and in series with the resistor 20 which is connected to terminal 30. The cathode 2 lo of the thyratron 2! is connected to terminal 29 and the plate 2| a is connected directly to the plate circuit of thyratron Hi. The screen grid l8b of the amplifier I8 is also connected to the screen grid [31) of the amplifier l3 and this tube I8 is stabilized thereby in the same manner as tube I3. Phototube l1 obtains its operating voltage supply also through terminal 36, which is in series with variable resistor 39 and resistor ll for supplying the potentials to the various dynodes of the phototube l1.

Also in the circuit is switch 42 which consists of a single-pole, three-position switch, shown in neutral position on contact 42b. The switch assembly includes the following contact points, terminal 4211. which is connected to the plate I3a of the amplifier [3, 42b which is unconnected and 420 which is connected to the plate l8a of the amplifier l8. Terminals 43 and 44 may be connected to a voltage supply which may be defollows: When switch 26 is closed, relay 25 is energized, causing the closureof terminals 25a and 25b and the opening of contacts 250 and 25d. When contact 25a is closed, the circuit between terminals 3! and 32 isscompleted andthe contactor of the X-ray machine is energized and X-rays are thereby produced. Phototube I! is placed behind a strip of fluorescentscreen which: fluoresces under the action of X-rays in a position immediately in the path of the projected X- ray beam which passes through the left chest of a patient standing in front ofthe device. Phot'otube l 'lis'place'd' behind a similar strip of fluorescent screen which i placed in a position directly in the projected beam of X-rays passing through theright chest. A cassette holding an X ray film is placed between the subject under examination and the phototube-screen assemblies so that simultaneously with the action of the X-rays upon the phototube-screen assembli'es X-rays are acting upon the film in the cassette;- When the switch 42'is in position 42b, the X-rays' passing through the subject under examination fall on the phototubes' l land ll, causing phototube current to flow through both of these tubes,- which collects on the respective condensers- I2 and 40. The resulting. potentials which develop-across'these condensers are applied to ther'espective amplifier tubes [3 and IB'and the amplified: voltage applied to the rids of the respectivethyratrons' l6 and 25'. As the-voltage on thecondensers I 2 and 40. increases as the amount of collected. chargev accumulates, a potential is eventually reached, at which one or the other of: the thyratrons will become conductive, causil'i'g current to? flow through the relay 22 and opening the? contact 2.2a of this relay. The circuit between terminals 3| and 32- is thereby broken, causing'the: deenergizin of the X-ray contactor andithetermination of the X-ray exposure. The thyratron' tube which will fire first,

that'iisrthyratron- IB orthyratron 2!, in this process will be determined by which phototube receives the'most-light. The phototube which re-- ceives the most light from its corresponding fiuoresc'e-ntscreem will. charge'up into the corresponding-condensermore rapidly and will cause its: thyratron tube to fire at the earlier time.

Therefore, should pathology be present in onelung, and not in the other andsince pathology reduces the radiolucency of the lung; it, therefore,. follows -tha-t-. the radiation. passing through the llOIll'lEtllllllg will causedetermination of the X-ray exposure.

If. switch. 42 is in position 42a, the amplified potential developedby the amplifier I3 is shortcircui'ted andphototube-I I thereby has noeffect on. the length of the X-ray exposure; that is, X-ray exposure is entirely'under the control of .4 the tube l1. Under this condition, the length of X-ray exposure is determined by the radiation passing through the right lung.

If switch 42 is in position 420, the amplifier tube He therefore is short-circuited and the control of exposure is under the influence of phototube II and, accordingly, the length of exposure is determined by the radiation passing through the left chest. Thus, by means of switch 42 it is possible to obtain exposure control photoelectrically for-v X-ray exposures by means of the radiation passing through the right lung or left lung or the more radiolucent of the two lungs.

Having thus described our invention, what we claim as new and wish to secure by Letters Patent is An X-ray photographic apparatus for simultaneously producing adjacent comparative photographs of adjacently disposed anatomical structures upon a single photographic film, and during a single exposure period, the duration of which is dependent upon the translucency of the objects photographed, said means including a single X-ray tube, connected in a power circuit, an X-ray'relay connected in a relay circuit and adapted to control said power circuit, electrically interrelated dual detection assemblies having identical functional characteristics, said assemblies having condenser thyratron circuits, 2. multiple switch relay including normally closed switches bridging each of said condensers, a normally open switchin said X-ray relay circuit for controlling said X-ray relay, and a normally open switch connected in the thyratron circuit, a direct circuit relay connected in said thyratron circuit, anormally closed switch in said X- ray relay circuit operated by'said direct current relay and in. series with the normally open switch in said X-ray relay circuit, said multiple switch relay operating to-effect the opening of the condenser switches, theclosing of the X-ray relay switch, and the closing of the direct current, thyratron circuit switch for the exposure period, and said direct current relay switch being adapted to openthe X-ray relay circuit with the firing of. the thyratron, and thereby terminate the propagation of X-rays.

RUSSELL H. MORGAN. PAUL C. HODGES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2;060,500 Hitchcock Nov. 10, 1936 2,401,289 Morgan et' al May 28, 1946 OTHER REFERENCES X-Ray Inspection with Phosphors and Photoelectric Tubes, by H. M, Smith, reprinted from the General Electric Review, issue of March 1945, vol. 48, No. 3, pp. 13-17, inclusive.

The Automatic Control of Exposure in Photofiuorography, by R. Morgan, Public Health Report, October 15, 1943, vol. 58, No. 43, pp. 1533- 1541. 

